Tamron SP 300mm F/2.8 LD (non-IF) Model 107B: The Model 107B is the original version of Tamron's SP 300 F/2.8 which was introduced in 1983. It was beautiful, expensive and is very rare since so very few were made during its one year production run. It does not feature the internal focus (IF) found in the later versions of this lens, but features very robust construction and is slightly heavier. This rare lens was finished in gloss white, is a very good lens for low light telephoto work, and is highly sought after as a collector's item. Two low dispersion (LD) elements are used in this lens, which I am pretty sure are the first (front) and the third element in the above optical layout. This lens also features a spherical aberration compensator group (the cemented doublet in the middle of the lens) which assures crisp images even at close focus distances.

Tamron unveiled a prototype of this lens (shown at right) at PMA 1982. The 107B prototype was finished in semi-gloss black, featured a built-in lens hood and a minimum aperture of F/22, and featured Tamron's scribed rubber focus grip rather than the diamond textured focus grip found on the production models. Notably, the prototype lens didn't feature a tripod socket. Tamron's representatives at PMA '82 described this lens as being designed to be "hand-held" rather than correctly explaining that the lens was merely a prototype!

Optically, the model 107B has slight inherent softness caused by very slight overcorrected spherical aberration which is introduced when using a rear drop-in standard filter. The extremely slight softness (when using the standard drop-in filter) makes this lens especially suitable for close-up portrait and stage photography whenever you don't want the finest of details rendered absolutely razor sharp. Removing the filter from the lens's rear filter holder makes the very slight spherical aberration disappear. The result is a significant increase in contrast and sharpness. Oops!!! Tamron's optical engineers originally designed this lens without accounting for the optical effects of the rear drop-in rear filter within the very fast F/2.8 optical path. The rear drop-in filter was added later during development after the initial optical design had already been "carved in stone". Remove the filter from the rear filter holder, and this gorgeous yet extremely rare lens will perform nearly as well as the model 60B introduced the following year. The later model 60B is somewhat sharper towards the corners and was designed to always be used with a filter in the rear filter slot. You can get the same slight softness effect with the later model 60B simply by removing the rear drop-in filter. The result will be slight undercorrected spherical aberration. The rear filter removal for this lens isn't merely a theory; I verified the results by testing my SP 300mm model 107B on my optical bench with 50x magnification at the focal plane. Shown further below are Modern Photography's test results with the filter along with my test results without the filter.

Lens Specifications:

Lens Model	107B
Focal Length	300mm
Aperture Range	f/2.8 — 32, AE
Angle of View	8°
Optical Construction (Groups / Elements)	6 / 7
Min. Focus from Film Plane	118" (3.0m)
Macro Mag. Ratio [w/2X Converter]	—
Filter Size	43mm (rear), 112mm (front)
Diameter	4.6" (117.5mm)
Length at [w/Nikon mount]	7.8" (199mm) [8.0" (203.5mm)]
Weight	73 oz. (2071g)
Lens Hood	Bayonet type #38FH, reversible.
Accessory	Accepts SP 2X tele-converter #01F. Supplied wth lens hood. Additional 43mm rear filters and 112mm front filter available as optional extras.